Cold-regulated genes under control of the cold sensor Hik33 in Synechocystis

A histidine kinase, Hik33, appears to sense decreases in temperature and to regulate the expression of certain cold-inducible genes in the cyanobacter ium Synechocystis sp. PCC6803. To examine the role of Hik33 in the regulati on of gene expression, we analysed a Delta Hik33 mutant using the DNA micro array technique. In wild-type cells, genes that were strongly induced at lo w temperature encoded proteins that were predominantly subunits of the tran scriptional and translational machinery. Most cold-repressible genes encode d components of the photosynthetic machinery. Mutation of the hik33 gene su ppressed the expression of some of these cold-regulated genes, which could be divided into three groups according to the effect of the mutation of hik 33. In the first group, regulation of gene expression by low temperature wa s totally abolished; in the second group, the extent of such regulation was reduced by half; end, in the third group, such regulation was totally unaf fected. These results suggest that expression of the genes in the first gro up is regulated solely by Hik33, expression of genes in the third group is regulated by an as yet unidentified cold sensor, end expression of genes in the second group is regulated by both these cold sensors.